The present invention relates to the protection of an electrical circuit against overload and here particularly against excess currents.
Overload protection for an electrical circuit may be provided directly through a circuit breaker which includes an armature for operating one or several pairs of contacts, particularly indirectly through release of another spring while acting against a return spring, the latter being stronger than the former but the former provides the requisite contact pressure. Moreover, the circuit breaker includes a magnetic core having an axial bore which traverses and penetrates the core entirely which bore is, therefore, accessible from the side facing away from the armature. The circuit breaker of the type mentioned thus far is, for example, described in German printed patent application No. 24 18 930.
Usually, circuit breakers are operated in such a manner that the current in the energizing coil increases until attracting the armature so that the armature in turn can cause the contacts to be closed. Following the electromagnetic attraction, the holding current through the energizing coil is reduced particularly for purposes of saving current, which is highly desirable, for example, in case a circuit pertains to a railless vehicle receiving power from electric batteries. Therefore, these kind of circuit breakers function essentially as electromagnetically operated devices. Therefore, they require supplemental elements in order to provide full protection of the normally goverened by the circuit breaker circuit. Consequently, the space requirement is fairly large, which again is undesirable in case of mobile equipment such as battery powered vehicles or the like.